Method of making leather



Patented Oct. 30, 1934 PATENT orrice 1,978,545 ME'ruon or MAKING LEATHER No Drawing. Application October 24, 1931, Serial No. 570,9

' Claims.

This invention relates to improvements in methods of making leather. While the invention is described with reference particularly to its application in the chrome tanning of skins, it is 'ning solution. After the tanning was completed,

the skins were removed from the drum and com-. monly stacked up on horses to drain, the draining of the work pieces being continued for many hours, usually over night, until they were dry enough to undergo a shaving operation to remove excess flesh from the flesh surfaces of the skins. Subsequently these same skins were introduced into the drum forthe second time for treatment with the desired coloring solution, usually an aniline dye. While still wet after coloring, the stock was subjected to fat-liquoring. No matter how well the skins may have been tanned by these prior methods, if they were not properly fat-liquored, they would dry out stiff and lack that full, well-nourished feel that is so esse'ntiall After this treatment they were usually set out by hand or by machine and then allowed to dry. Commonly they were again dampened or sammied by being piled in damp sawdust and subsequently staked in order to stretch and soften them. The sammied and staked leather was then stretched on a frame or board and tacked all around the edge and allowed to dry.

Because of the drumming of the skins, in large numbers, continued for many hours there was very considerable shrinkage in the area of the skins, probably due in part to slow tanning and in part to the heat developed during the long continued pounding of the skins in the closed drums. This loss in area commonly amounted to as much as ,to as compared with the area of the skin if lightly slicked out fresh from the'pickle or salt solution. Because of the lengthy draining of the skins after the tanning operation, a very marked lack of uniformity in the skins resulted, due in part to the fact that some of the skinswere subjected to heavier pressure than those above them in the pile and to the fact that the top skins of the pile were subjected to a greater degree of evaporation in the atmosphere. Since the skins were fleshed or shaved after the tanning operation, that is, after one drumming operation, they had to be returned to the drum for the dyeing operation, this rehandling of the skins involving time and labor which increased substantially the cost of production of the leather. Another disadvantage of prior methods resided in the necessity of stretching and securing the skins in stretched-out condition upon drying boards. This is not only a laborious and time-consuming operation but it necessitates the cutting away of perforated or otherwisemarred margins of the hides or skins, thus reducing substantially the area of the tanned and dyed goods. An even greater disadvantage of this method of drying the skins resides in the fact thatthere is an entire lack of uniformity in the stretching effect on all the various portions of the skin, this ununiform tension being an important factor in the production of unsatisfactory leather.

Objects of the invention are to obviate the disadvantages of methods of leather manufacturing as heretofore commonly practised and to pr duce as compared with the results of such 3:. 0

practice a greater area of leather from the skins together with a substantial increase in the quality as evidenced by increased thickness of the tanned skins, a better feel of the leather due to greater flexibility and softness and, finally, a better appearance of the grain surface. Other objects of the invention are to minimize handling of the work pieces, to shorten very substantially the time necessary for making finished leather from skins and, in certain cases, to eliminate several operations heretofore considered requisite, thus simplifying the process, lessening very materially the labor involved, and reducing the costs, as compared with the results commonly obtained in the past. 95.

To these ends, and in accordance with important characteristics of the invention, the skins are preferably first subjected to a fleshing operation after removal from the pickle or from a preservative salt solution following the pickle. This fleshing operation is designed to remove flesh particles and connective tissue from the flesh surfaces of the skins and to secure a fine even appearance of the flesh surfaces. of the work pieces prior to their introduction into the drum so that not only the tanning but the dyeing operation may take place before the skins are removed from the drum. According to methods heretofore practised, the skins, which had been fleshed after liming, had also to be fleshed or shaved after the tanning operation, or after a partial tanning, before they could be dyed, for it they were fleshed or shaved after dyeing the flesh surfaces would appear very ununiform in color since the dyeing, as heretofore carried out, was largely a surface coloring. By fleshing from the pickle and before tanning and dyeing only one introduction of the skins into the drum is necessary, thereby saving all the labor and time involved in removing the skins after the tanning and reintroducing them for a dyeing operation. Furthermore there are avoided the ill effects of the horsing-up and draining as heretofore practised after tanning. It will be understood that in certain cases and with certain grades of skins, the manufacturer may dispense with the fleshing operation after the pickle, even though it is preferable for the best grades of work since in the latter case the flesh surfaces of the tanned and dyed skins will have a finer and more uniform color.

The skins, after the fleshing operation, are preferably introduced in relatively small numbers into drums which are advantageously much smaller and better ventilated than the drums heretofore commonly used in tanning operations. It has been found that by drumming the skins in smaller batches and with a tanning solution at least as strong as, but preferably much stronger than, that commonly employed the leather obtained is of better quality and of substantially greater area per skin. This is due in part to the fact that with smaller batches the skins do not receive the heavy pounding that accompanies the drumming of the skins in large batches. By drumming in a strong tanning solution and maintaining a high degree of ventilation the tanning operation may be completed in a much shorter" time, and the formation of heat and the consequent shrinkage of the skins (so commonly experienced in the past) may be greatly reduced or even entirely obviated.

Since the tanning and dyeing may take place in the same drum, with or without a washing operation between the application of tanning and dyeing materials, it is clear that the time and the labor involved are greatly reduced, as compared with prior methods. Furthermore, washing and draining may take place in the drum, thus obviating any necessity for the long-continued draining so commonly practised by horsing-up the skins for overnight draining.

In accordance with a preferred method of tanning, the tanning materials are first wrapped in sheet material such as paper, prepared by wax or otherwise to be resistant to acids, alkalis, and other chemicals, and the paper-wrapped bun-' dle may then be secured in a suitable fabric bag, the calculated amount for a given batch of hides or skins being-wrapped up in one or more bags for introduction into the drum. During the drumming operation, the tanning materials gradually escape from the waxed paper, which is frangible, and from the bag into the usual salt solution provided for the purpose of carrying the tanning material to the skins. Since the tanning compound begins to act on the skins as soon as any portion thereof is dissolved, the tanning solution is of moderate strength at the beginning and is gradually and continuousli strengthened without any attention on the part of the workman. Furthermore, the tanning material is uniformly distributed in the drumming and secures uniform results in the tanned skins. By using measured amounts of tanning, dyeing,

and reducing agent materials in bags, the work and the responsibility of the operator is greatly reduced and simplified so that ordinary tannery workers may be assigned to the job, whereas, heretofore. expert operators have been required in chrome tanning, and particularly in dyeing operations in connection with both chrome and vegetable tanning.

At the end of the tanning, dyeing, washing, and draining operations, all preferably carried on in the same drum, the skins are removed and preferably are slicked-out individually upon smooth work supporting surfaces to secure the desired area and to remove part of the watery content. Conveniently, this slicking-out operation is performed on a portable and flexible work support. The work support is portable so that it, and the skin slicked-out thereon, may be transferred to a drying support with the skin in contact with the drying support, so that the skin may be stripped from the work support and left in fully slicked-out condition on the drying support. The work support is preferably flexible to facilitate the stripping operation since in the case of a flexible work support it is the latter which is stripped or peeled from the skin, leaving the latter in fully extended condition on the drying support. It will be noted that in the practice of the invention there is only one drying operation whereas, in the preparation of finished leather by prior methods, two dryings were necessary.

The above and other important characteristics of the invention will now be described in detail in the specification and then pointed out in the appended claims.

In practising this improved method of converting skins into finished leather, the skins are prepared-for the tanning operation in the usual manner with an exception which will hereinafter be described in detail. In the usual preliminary preparation there is included the steps of soaking the skins to clean them and to make them soft and pliable after which they are subjected to the limes for the purpose of loosening the hair or wool. Following the liming operation, the skins are unhaired either by a hand tool or by the use of a suitable unhairing machine. Following the unhairing operation the skins are commonly subjected to a fleshing after which they are subjected to bating, and drenching or pickling operations. Commonly, sheepskins are degreased either before or after pickling by subjecting them to heavy pressure in a press. In the past the skins have gone directly from the pickling. or from the degreasing operation in the cast of sheepskins. to the tanning drum particularly in the case of chrome tanning operations. It is at this point that the improved method diverges sharply from the practice of the past. According to the improved method. the skins are subjected to an additional fleshing operation after the pickle designed to leave the flesh surface of each skin in such condition that it will take a fine uniform color during and following tanning and dyeing operations. Heretofore the skins have been tanned and then subjected to a fieshing or shaving operation before being treated with the selected dye material. Since the dyeing operation is ordinarily carried out in a drum it follows that the skins, particularly in chrome tanning operations, were introduced twice into the drum first for tanning and later for the dyeing operation. This involved a great amount of time and labor. By fieshing the skins from the pickle both tanning and dyeing operations may be carried out in the skins.

same drum. Since the skins after pickling are thinner and firmer than'after liming (when the first fieshing operation 'is performed) this second fleshing obtains results quite similar to the shaving of tanned skins. The fieshing operation is preferably carried out according to a method disclosed and claimed in application Serial No. 584,570, filed January 2, 1932 in the names of M. M. Merritt and N. H. Poor.

After the fleshing operation the skins are conveniently introduced into'a drum for the tanning and dyeing operations. While a drum of any wellknown construction may be employed it is preferable to utilize a drum which is well ventilated and which is so constructed as to permit the ready introduction and removal of the skins and of the various materials and/or solutions used in the, tanning, dyeing, washing and draining operations.

In general the drum should be considerably smaller than those ordinarily employed in tanning operations since it is desirable to drum the skins in smaller batches for the reason that with large drums and large batches of skins, the latter receive such severe pounding during the drumming operations as to retard the penetration of the tanning materials into the substance of' the Furthermore, more time is apparently necessary with the big drum to secure thorough penetration of the tanning liquids. with greater chances of heating the skins during drumming.

Due to the slower penetration of the tanning liquids into the skins, to the development of heat during the tanning operations, and to the pounding to which the contents of the drum is subjected, the skins thus treated in the big drum suffer a very considerable shrinkage in area and the quality of the leather is often undesirable and even inferior. It is for these reasons that skins in accordance with the improved method are drummed in batches of about five or six dozen, and in a comparatively small drum where the skins are not dropped such heights and are not pounded so severely as they would be in the larger drums. Preferably also the tanning liquid is limited in amount, approximately a gallon to each dozen skins. Moreover, the drum is well ventilated so that it is possible to use tanning solutions of a strength greater than heretofore to effect thorough permeation on the skin substance in a relatively very short time without overheating or other detrimental effects.

Preferably the tanning material includes a chromium salt and sulphuric acid, the latter in the form of the concentrated acid which may be mixed directly with the chromium compound or dispersed through a suitable quantity of absorbent material such as shredded blotting paper. The chromium salt and the acid are enclosed in a paper, waxed or otherwise prepared to withstand the action of acids and alkalis. The package in its waxed paper is then introduced into a bag, of cotton or other fabric, whichis sewed or tied so as to secure and retain the paper after the dissolution of the chemicals within. It is preferable to put the dye material up in a separate package, in which case the'dye solution is conveniently mixed with paper pulp preliminarily to being wrapped in waxed paper and fastened in a cotton bag. By thus packaging the tanning and dyeing materials, it is insured as far possible that the workmen will use exactly the required amount of tanning and dyeing materials for the batch of hides or skins in the drum. Furthermore, the amount of tanning and dyeing material is nicely calculated to give the best reare distributed gradually and continuously to the drum contents from the package there is secured uniform and highly effective tanning and dyeing results, the tanning material, particularly, being taken up by the hides or skins at a rate approaching closely to the rate at which said material is dissolved.

The tanning and dyeing operations in the drum will now be described step by step beginning with the introduction of five dozen sheepskins into,the drum. These skins, as stated above, have been fleshed from the pickle and are introduced into the drum with about five gallons of 40 Bkr. salt solution. The drum is then set in rotation and through an opening therein there is thrown a bag containing the proper measured amount of a chrome tanning compound which escapes gradually from the bag, since the waxed paper is frangible and the bag of porous material, and mcoming dissolved in the watery contents of the sults. As the tanning and/or dyeing materials drum is carried to the hides or skins as fast as after its introduction into the drum, and penetra- ,tion of the skins by the tanning material, which begins very soon after the said material is introduced, is completed in about half an hour. Then, with'or without washing of the skins thus treated,

there is introduced into the drum the requisite amount of a reducing agent. tendency for the skins to become thin and hard, they should .be well washed after the tanning treatment and before adding a reducing agent. Commonly thiosulphate of soda is used for this purpose and may be put up in a measured amount in waxed paper and in a cotton bag, about300 ounces for five dozen sheepskins. If desired, however, this salt commonly called hypo? may be introduced in solution since it is a cheap material, easy to handle, and the amount may vary considerably on the excess side without deleterious results. However, it is. preferable to introduce the hypo in waxed paper and a bagsince it is then applied gradually and evenly thus securing the best results as indicated by uniformity in the color of the skins at this stage of their treatment. After the introduction of the hypo, drumming is continued for another half hour, at the end of which time the chromium will be reduced throughout the substance of the skins. Without removing the skins from the drum they are thoroughly washed by introducing plenty of wash water and draining, the washing operation being continuous to remove most efliciently any excess tanning material or "hypo, the whole operation requiring not more than ten minutes.

The packag ng and/or bagging of materials used in tanning and dyeing operations is applicable to other tannages besides chrome and to other substances, besides dyes and reducing agents, used in the treatment of hides and skins.

At the completion of the tanning operation the skins will be thoroughly washed with water and drained while in the drum, enough of the water being retained after the final washing to act as a If there is any' solution for dye material in those cases wherein the dyeing is performed after, and not during, the tanning operation. The amount of dye material will vary with the dye material employed and with the shade desired. For a simple color like Leather tan" about nine ounces of the dye will be dissolved in four gallons of boiling water, cooled and strained before being introduced into the drum. Following the dyeing the skins are again washed and drained, all of the tanning, dyeing, washin and draining operations being carried out upon the skins after they have once been introduced into the drum. Following the draining operation they are ready to. be removed from the drum.

After being removed from the drum, the skins are slickcd-out individually upon a smooth work supporting surface. Preferably the work support is a portable and flexible mat such as a sheet of rubber or linoleum. The slicking-out oporation is performed thoroughly to obtain the fully extended area of the skin and to remove a part of the watery content of the skin. This slicking operation may be done by hand with a slicking tool or by a suitable machine. Usually the grain surface is in contact with the mat espccially when the' putting-out operation is per formed by a machine. The portabie work support with the skin slicked-out thereon is promptly transferred to a. drying support with the skin in contact with the latter. An edge portion of the skin is loosened from the work support or mat and the latter being flexible, is stripped or peeled away from the skin, leaving the latter in fully slicked-out condition upon the drying support. When this skin has dried on the drying support it will be found to be thoroughly tanned. It will dry practically without shrinking and the quality as indicated by weight, flexibility, and appearance of the grain is markedly above the best leather produced by prior methods. While the skin may be secured to the drying board with light staples, other means or methods may be employed for the purpose.

Having described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. That improvement in methods of tanning and dyeing skins which comprises subjecting skins in a drum to achromium tanning solution for the desired length of time, subjecting the skins in the drum to the proper amount of a reducing agent in solution to reduce the chromium within the substance of the skins, then washing the skins thoroughly and draining in the drum, while the skins in the drum are still wet subjecting them to a solution of a dye until the dye mat rial has penetrated the skins, and again draining them, the operations being carried out while the skins are in the drum. 1

2. That improvement in methods of treating skins, that have received preliminary treatment ncluding liming, fleshing and pickling, which comprises fleshing the skins from the pickle, and then treating these fleshed skins with a tanning solution until they are thoroughly tanned a uniform color.

3. That improvement in methods of treating skins, that have received pre iminary treatment including liming, fleshing and pickling, which comprises fleshing the skins from the pickle, and then treating these fleshed skins with suitable tanning and dyeing solutions until they are thoroughly tanned and dyed a uniform color.

4. That improvement in methods of tanning skins, that have received preliminary treatment including liming, fleshing and pickling, which comprises fleshing a skin from the pickle, subjecting the skin to drumming with a chromium tanning solution for the desired length of time, and while the skins are still in the drum introducing a suitable dye and drumming until the dye material has penetrated the skins.

5. That improvement in methods of tanning and dyeing skins, that have received preliminary treatment including liming, fleshing and pickling, which comprises fleshing the skins from the pickle, subjecting the skins to drumming with a chromium tanning solution for the desired length of time, introducing a reducing agent and continuing the drumming, then washing the skins thoroughly, and while the skins are still in the drumintroducing a suitable dye and drumming until the dye material has colored the skins.

6. That improvement in methods of making leather from skins, that have received preliminary treatment including liming, fleshing and pickling, which comprises fleshing the skins from the pickle, subjecting the skins to a chromium tanning solution for the desired length of time, then to a reducing agent, then washing thoroughly, while the skins are still wet subjecting them to a solution of a suitable dye until the dye material has colored the skins, washing and draining the skins in the drum, and then promptly slicking-out each skin to smooth out the grain surface and to remove a part of the watery content thereof preparatory to drying the skins.

7. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of salt solution, introducing into the drum a chromium tanning compound and a dye both in a substantially dry condition and contained in a porous bag in amounts calculated as sub stantially just sufiicient to tan-and dye the skins in the drum, and rotating the drum whereby the chromium compound and the dye are dissolved in the bag and gradually diffused from the bag throughout the water content of the drum and simultaneously applied to the skins therein, whereby the tanning and dyeing solutions are of moderate strength at the beginning and are gradually increased in strength as the drumming is continued.

8. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of salt solution, wrapping up in a frangible acidand alkali-resisting sheet a calculated amount of chromium tanning compound, placing the package thus made in a fabric bag, introducing the bag into the drum, rotating the drum whereby the wrapping sheet is ruptured, the chromium tanning compound dissolved in the bag and diffused throughout the water content of the drum and simultaneously applied to the skins therein, the drumming being continued until the skins are thoroughly permeated with the chromium tanning compound, and then adding a reducing agent in the proper amount to secure reduction of the chromium within the substance of the skins.

9. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of salt solution, wrapping up in waxed paper a calculated amount of a chromium tanning compound, placing the waxed paper package in a fabric bag, introducing the bag into the drum, and rotating the drum whereby the wrapping sheet is ruptured, the chromium compound dissolved in the bag and difiused throughout the water content of the drum and simultaneously applied to the skins therein, the drumming being continued until the skins are thoroughly permeated with the chromium solution.

10. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of salt solution, wrapping up in waxed paper a calculated amount of a chromium compound, and an acid distributed through a mass of inert absorbent material, placing the waxed paper package in a fabric bag, introducing the bag into the drum, rotating the drum whereby the wrapping sheet is ruptured, the chromium com-,

pound and the acid dissolved in the bag and diffused throughout the water content of the drum and simultaneously applied to the skins therein, the drumming being continued until the skins are thoroughly permeated with the chromium and acid solution, and then adding a reducing agent in th proper amount-to secure reduction of the chromium within the substance of the skins.

11. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of water, wrapping up in a frangible acid and alkali-resisting sheet a calculated amount of a tanning compound, placing the package thus made in a fabric bag-introducing the bag into the drum, and rotating the drum whereby the wrapping sheet is progressively broken up and the tanning compound is diffused from the bag throughout the water content of the drum and simultanenously applied to the skins therein.

12. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of water, wrapping up in waxed paper a calculated amount of a tanning compound, plac-- ing the waxed paper package in a fabric bag, introducing the bag into the drum, and rotating the drum whereby the wrapping sheet is progressively broken up and the tanning compound is diffused from the bag throughout the water content of the drum and simultaneously applied to the skins therein.

13. That improvement in methods of tanning skins which comprises placing a predetermined number of skins in a drum with the desired amount of water, placing in a fabric bag a tanning compound in an amount calculated as just sufficient to tan the skin, introducing the bag into the drum, and rotating the drum whereby the tanning compound is difiused from the bag and throughout the water content of the drum and simultaneously applied to the skins therein in gradually increasing strength.

14. :That improvement in methods of tanning skins which comprises placing a number of skins in a container with a restricted amount of liquid, introducing into the container a tanning compound in solid form and in an amount just sufiicient completely to tan the skins, the said tanning compound being contained in a pervious receptacle from which it diffuses upon agitation in the said liquid, and agitating the skins and the tanning compound in the liquid to dissolve the compound and apply it gradually and continuously to the skins.

15. That improvement in methods of tanning skins which comprises introducing a predetermined limited number of skins into a drum, providing a tanning compound in anamount calculatedas just sufiicient completely to tan the skins in the drum in water amounting to substantially a gallon for each dozen skins, and rotating the drum to cause penetration of the skins by the tanning compound.

16. That improvement in the method of tanning skins which comprises placing in a drum a batch of skins not substantially less than five dozen in number nor substantially more than ten dozen, introducing'a tanning compound in an amount calculated as just suificient completely to tan the skins in the drum in water amounting to substantially one gallon for each dozen of skins, and drumming the skins to cause penetration thereof by the tanning compound. 

